Genetic structure in relation to movements in wild European grayling (Thymallus thymallus) in three Norwegian rivers

Abstract

The relationship among genetic structure, movements, and barriers was studied in European grayling (Thymallus thymallus). Gene flow is closely related to movement patterns, and genetic differentiation may be negatively correlated with movement. Grayling movements in the Glomma River (8149 tagged) and the neighboring Trysilelva River (4070 tagged) were different among sampling sites. Most individuals were stationary (±0.5 km), but some individuals moved long distances (≤153 km). The movement data indicated potential for gene flow between the two upstream sampling sites in the Glomma River and between the two midstream sites in the Trysilelva River. Allele frequencies at seven microsatellite loci indicated pairwise differentiation across sampling sites. Genetic structuring was generally consistent with the observed movement pattern. Isolation-by-linear-distance or number of potential barriers (dams, lakes) was not significant among sites within streams or among sites within the two southern streams. They were significant, however, if two outlying northern populations in the Pasvik River were included. Our results suggest that although grayling may move long distances, they also exhibit genetic structuring within large continuous river systems. Fish movement, often the result of flexible and adaptive behavioral strategies, is the ecological mechanism for gene flow. Movements may be the adaptive link explaining how environmental conditions affect genetic structuring.